The present invention relates to an optical fiber unit structure for use in an optical submarine cable system.
An optical fiber submarine cable must be designed so that the transmission and mechanical characteristics of the optical fiber used as a transmission medium may not deteriorate for as long a time as 20 years or more. To meet this requirement, it is usual practice in the art to house the optical fiber in a pressure resisting structure to protect it from a sea water pressure as high as 800 atmospheres.
In optical fiber submarine cables, the optical fibers are normally protected from sea water as described previously but, when the cable is broken through an accident, sea water enters into the cable. To avoid this, it has been proposed, for instance, to fill up a gap between the optical fiber unit and the pressure resisting structure with a jelly-like substance. However, sea water also enters into the optical fiber unit from its end portion.